| DICOM PS3.5 2024d - Data Structures and Encoding |
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DICOM provides a mechanism for supporting the use of JPEG XL Image Compression through the Encapsulated Format. Annex A defines a number of Transfer Syntaxes that reference the JPEG XL Standard. The JPEG XL Lossless Transfer Syntax provides a compression scheme that preserves the bits of the original image, i.e., lossless. The JPEG XL JPEG Recompression Transfer Syntax preserves the bits of the (lossy) JPEG encoding. The JPEG XL Transfer Syntax is a potentially lossy compression of the original image.
The context where the usage of lossy compression of medical images is clinically acceptable is beyond the scope of the DICOM Standard. The policies associated with the selection of appropriate compression parameters (e.g., compression ratio) for JPEG XL lossy compression are also beyond the scope of this Standard.
The use of the DICOM Encapsulated Format to support JPEG XL Compressed Pixel Data requires that the Data Elements that are related to the Pixel Data encoding (e.g., Photometric Interpretation, Samples per Pixel, Planar Configuration, Bits Allocated, Bits Stored, High Bit, Pixel Representation, Rows, Columns, etc.) shall contain Values that are consistent with the characteristics of the compressed data stream. The Pixel Data characteristics included in the JPEG XL bit stream shall be used to decode the compressed data stream.
The requirements when using a Standard Photometric Interpretation (i.e., a Defined Term from Section C.7.6.3.1.2 in PS3.3 ) are specified in Table 8.2.15-1. No other Standard Photometric Interpretation values shall be used.
Table 8.2.15-1. Valid Values of Pixel Data Related Attributes for JPEG XL Transfer Syntaxes using Standard Photometric Interpretations
These requirements are specified in terms of consistency with what is encapsulated, rather than in terms of the uncompressed pixel data from which the compressed data stream may have been derived.
When decompressing, should the characteristics explicitly specified in the compressed data stream be inconsistent with those specified in the DICOM Data Elements, those explicitly specified in the compressed data stream should be used to control the decompression. The DICOM Data Elements, if inconsistent, can be regarded as suggestions as to the form in which an uncompressed Data Set might be encoded, subject to the general and IOD-specific rules for uncompressed Photometric Interpretation and Planar Configuration, which may require that decompressed data be converted to one of the permitted forms.
PS3.3 may constrain the values of Photometric Interpretation for specific IODs.
The JPEG XL bit stream is capable of encoding both signed and unsigned pixel values, hence the value of Pixel Representation (0028,0103) may be either 0 or 1 for monochrome Photometric Interpretations depending on what has been encoded.
The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in the JPEG XL standard, hence it shall be set to 0.
| DICOM PS3.5 2024d - Data Structures and Encoding |
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